Primordial Dirac leptogenesis

We present a novel realization of Dirac leptogenesis based on the postinflationary reheating phase of the early Universe. An asymmetry generated within the scalar sector via <a:math xmlns:a="http://www.w3.org/1998/Math/MathML" display="inline"> <a:mi>C</a:mi> <a:mi>P</a:mi> </a:math> -violating and out-of-equilibrium inflaton decays is transferred to chiral neutrinos through Yukawa interactions and then to baryons via electroweak sphalerons. We describe in detail a minimal realization of this mechanism that naturally accommodates small neutrino Yukawa couplings and results in contributions to the effective number of relativistic species, <c:math xmlns:c="http://www.w3.org/1998/Math/MathML" display="inline"> <c:msub> <c:mi>N</c:mi> <c:mi>eff</c:mi> </c:msub> </c:math> , testable in upcoming cosmological observations.